A company will buy or build a set of apartment blocks or condos and then allow investors to buy them through the company, thus joining the group. 

A single investor can own one or multiple units of self-contained living space, but the company operating the investment group collectively manages all the units, taking care of maintenance, advertising vacant units and interviewing tenants. 

In exchange for this management, the company takes a percentage of the monthly rent.

There are several versions of investment groups, but in the standard version, the lease is in the investor's name and all of the units pool a portion of the rent to guard against occasional vacancies, meaning that you will receive enough to pay the mortgage even if your unit is empty. 

The quality of an investment group depends entirely on the company offering it. In theory, it is a safe way to get into real estate investment, but groups are vulnerable to the same fees that haunt the mutual fund industry. 

Once again, research is the key.